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Brake indicator is OFF with no pressure on the front or the rear brakes. Brake indicator is OFF with equal pressure on the front or the rear brakes. Brake indicator is ON with unequal pressure between the front and the rear brakes. You will need something that senses, both front and rear pressures at the same time, otherwise brake indicator will not work properly. I'm not sure how a YJ prop valve works. Is there something different?

200vac range is high for this reading. Set a 20vac range. Should see up to 2.5vac reading. EDIT: I see you changed ranges.

AC scale for voltage check.

Seem like you're running a coolant temperature sender (used for gauge), instead of a coolant temperature switch (used for idiot light).

Here's a couple RENIX publications you might find useful. RENIX_MPI 88 MJ ELECTRICAL MANUAL

Cats don't like rich. Perform Cruiser54 tip #1, before replacing any parts. Cruiser54 Tips

No. I meant the tube that runs from the front of the air box to the exhaust manifold flange. EDIT: OK. Now I see what you are saying. I understand.

Does it get brighter as the engine warms up?

The possibility for running rich are many. What do the spark plugs look like? Are all vacuum lines secure and not leaking? etc etc.

Even a faulty hot air intake valve shouldn't starve the engine of air. Hooking up the flex tube killed the engine. What was inside that flex tube? Was it stuffed with 'cursed' money? Luckily, you didn't burn down the vehicle.

Running Rich: Unburnt fuel in exhaust. Soot on inside tailpipe. Burning sensation in the eyes. Vehicles driving behind you slow down or attempt to pass you quickly. A new catalytic converters will not solve this problem.

Running rich kind of fumy?

Good find. Never underestimate the value of the visual inspection.

Check manifold vacuum using a vacuum gauge. While cranking fuel pressure should drop as manifold vacuum increases. EDIT: With throttle plate closed.

If you got two wires that go from the CPS to and through the firewall, vehicle has TSB fix for CPS. This fix took CPS wiring directly to the ECU. Drop ECU and visually check CPS wiring at the ECU. Make sure both wires are connected and terminated properly. Easy check before new CPS arrives.

CPS (Crank Position Sensor) = Engine Speed Sensor.

Not sure if this test would be correct. It still don't tell if Cyl #1 is on compression. Wouldn't you get the same results if timing light was connected to Cyl #6? Still can't tell if its compression or exhaust stoke.

C109 is a inline connector (engine harness to engine control harness) located on the right side of the engine bay. Sync Sensor is C231 and ground pin is "A" (harness side).

Yes

Look for path to ground at the sync sensor (C231_A harness side). If missing 4 pin connector is C109, then no path to ground. Added: You still need to determine if Cyl #1 is on compression stoke or exhaust stoke. Your pictures don't prove that.

Find that connectors mate. It can't be too far away. Unable to tell if you're showing the Engine Harness side connector or the Engine Control side harness connector, either way, find its mate.

Noted: Thanks

Isn't there a vacuum dump valve on the brake pedal for the cruise control?

Photo taken from 88 electrical manual (flip to keep the tap side up as in above photo's). Vehicle harness side: Pin A - Sensor ground Pin B - IAT signal Here PIn A = Pin 1 and Pin B = Pin 2. Something is not right, call out table is different then 88 ETM or 88 ETM is different then call out table. Hope this helps (to add to the confusion). My guess: Purple (IAT signal).